The present invention relates to a test plug for testing the integrity of a pipe.
Test plugs are used to isolate lengths of a pipe to test the integrity of the pipe or of welds or flanged connections within the length of pipe being tested. Conventional prior art test plugs use elastomeric seals which are compressed to seal the test plug against the inside surface of the pipe. In one example, in Canadian Patent No. 1,312,557, the elastomeric seal is cylindrical and is compressed from both ends to force the seal to bulge outwards. In U.S. Pat. No. 5,844,127, the elastomeric seals are O-rings which are circular in cross-section. The O-rings are squeezed between outwardly bevelled surfaces to force the O-ring to bulge outwards.
One difficulty with prior art test plugs is the need for a wide assortment of plugs for varying diameters of pipe. A single test plug cannot accommodate a wide variety of pipe diameters because the test plug must have sufficient clearance to be inserted into the pipe and can only expand to a certain size, beyond which a tight seal does not form.
As well, test plugs with elastomeric seals cannot be used with high pressure testing because of the limited grip of the seal against the inside of the pipe. Other prior art test plugs solve this problem with the use of metal dogs which grip the pipe, such as those disclosed in Canadian Patent No. 1176189. Metal dogs however can damage the inside surface of the pipe.
Therefore, there is a need in the art for an improved test plug which mitigates the difficulties of the prior art.
The present invention is directed to a test plug apparatus for sealing the inside of a pipe for isolating or testing the integrity of a portion of the pipe. In one embodiment, the apparatus comprises:
(a) a blind flange for mating with a flange attached to a proximal end of the pipe, said blind flange having a threaded inner bore;
(b) a positioner comprising:
i. an inner bore, a proximal end and a distal end;
ii. a hydrotest port in the proximal end which provides fluid communication of a pressring floid through the positioner; and
iii. a threaded exterior surface which engages the inner bore of the blind flange;
(c) a compression mandrel having a proximal end, a distal end and an inner bore, wherein the proximal end engages the distal end of the positioner, the inner bore is continuous with the inner bore of the positioner, and the distal end comprises a conical recess and a removeable annular compression ring;
(d) an expander with core having a conical seal expanding surface and a removeable annular compression ring;
(e) means for actuating the expander positioned within the inner bore of the positioner and the compression mandrel; and
(f) an elastomeric annular seal which is circumferentially mounted on the expander cone and positioned between the compression rings.
In one embodiment, the actuating means comprises an actuator rod having a proximal end and a distal end and a coupling sleeve, wherein said actuator rod passes through the inner bore of the positioner and the compression mandrel and said coupling sleeve is affixed to the distal end of the actuator rod and threadingly engages an expander shaft.
Preferably, the seal element and compression rings are chosen from a plurality of seal elements and compression rings having different outside diameters to match the inside diameter of the pipe to be tested.
In another embodiment, the invention comprises a test plug apparatus comprising a sealing mechanism comprising:
(a) a compression mandrel defining an internal bore and a conical recess and having a removeable compression ring;
(b) an expander element comprising a conical seal expander and a removeable compression ring, wherein said conical seal expander mates with the conical recess of the compression mandrel;
(c) an annular elastomeric seal which fits over the conical seal expander and between the compression rings;
(d) means for displacing the expander element relative to the compression mandrel;
(e) wherein the seal is expanded over the conical seal expander and compressed between the compression rings when the expander element is moved towards the compression mandrel.
The displacement means preferably, but not necessarily, comprises an actuator rod and a threaded coupling which is mounted to the actuator rod and which mates with an expander shaft which is attached to the expander element.
In another aspect of the invention, the invention comprises a method of pressure testing a pipe to which an end flange has been welded, comprising the steps of:
(a) providing test plug sealing assembly comprising a compression mandrel defining an internal bore and a conical recess and having a removeable compression ring; an expander element comprising a conical seal expander and a removeable compression ring, wherein said conical seal expander mates with the conical recess of the compression mandrel; an annular elastomeric seal which fits over the conical seal expander and between the compression rings; and means for displacing the expander element relative to the compression mandrel;
(b) mounting a positioner into a blind flange and mounting the sealing assembly to the positioner;
(c) mounting the blind flange to the end flange such that the sealing assembly is inside the pipe;
(d) actuating the seal by displacing the expander element;
(e) pressurizing the annular space between the sealing assembly and the pipe (the test space); with a pressurized test fluid and
(f) checking for pressure integrity.